Process for the preparation of flameretardant silicone rubber and composition thereof



United States Patent Richard M. Savage, Latham, N.Y., h ssignor toGeneral Electric Company, a corporation of New York No Drawing.Application February 7, 1956 e Serial No. 563,838

17 Claims. (Cl. 260-37) This invention is concerned withorganopolysiloxanes having improved flame-retardant properties. Moreparticularly, the invention is concerned with a composition of matterwhich in the cured state exhibits improved flame-retardant properties,which composition comprises (1) an organopolysiloxane convertible to thecured, solid, elastic state consisting essentially of silicon atoms,oxygen atoms, methyl groups, and an aromatic radical selected from theclass consistingof aryl and halogenated aryl radicals, the saidorganopolysiloxane containing from 3 to 35 mol percent silicon-bondedaryl or halogenated aryl groups of the total number of silicon-bondedorganic groups, there being present from 1.98 to 2.05 organic groups persilicon atom, (2) a finely divided inorganic filler, and (3) a finelydivided cupreous material present in amounts sufiicient to impartflame-retardant properties to the cured, solid, elasticorganopolysiloxane, the said cupreous material being selected from theclass consisting of copper, copper halides (both cupric and cuproushalides), copper oxides (e.g., cuprous oxide, cupric oxide, etc.), andmixtures of the aforesaid cupreous materials.

Vulcanized (or cured), solid, elastic organopolysiloxanes (for brevityhereinafter referred to as silicone rubbers), whether vulcanized bymeans of heat in the presence of organic peroxides or other organiccuring agents, or when vulcanized in accordance with high energyelectrons described in Lawton and Bueche patent application Serial No.291,542, filed June 3, 1952, are known to have good heat resistance atelevated temperatures of from 150 to 200 C. or higher. However, incertain applications, particularly in coating applications, it has beenfound that these silicone rubbers, at temperatures encountered by directcontact with an open flame, do not have the desired flame retardancyproperties which some applications may require when the silicone rubberis ignited. r 3

Due to the presence of organic groups in the organopolysiloxanestructure, once a flame is applied to silicone rubber, even though it isfilled with an inorganic filler such as finely divided forms of silicondioxide or calcium carbonate, the silicone rubber will continue to burnunless extinguished by external means, and will be ultimately almost100% consumed. Conditions of this type where flame retardancy is animportant requirement of a molded or extruded article may be found inthe aircraft and other industries, particularly in connection withgrommets, seals or gaskets; or as insulation on electrical conductorswhere high degrees of fiame-retardancy are an essential requirement. r

I have now discovered that I am able to improve the flame-retardantproperties of silicone rubber by incorporating therein varying amounts,for instance, from about 0.25 to 20%, by weight, based on the weight ofthe convertible organopolysiloxane, of a cupreous material selected fromthe class consisting of finely divided copper, cuprous oxide, cupricoxide, copper halides, and mixtures of said cupreous materials, in whichthe proportions of the cupreous material are that described above. By

2,891,033 Patented June 16, 19 59 means of the incorporation of minoramounts of the cupreous material, I am able to greatly improve the flameretardant properties of the silicone rubber. In the ab: sence of thefinely divided cupreous material, the silicone rubber generally willburn, even though there are present in the silicone rubber relativelylarge amounts of inorganic flame-resistant fillers. The fact that thesecupreous materials have the ability to improve the flame-retardantproperties of the filled silicone rubber was unexpectedly andunpredictably found to be specific to the finely divided cupreousmaterial, since the use of other fiame retardant materials, particularlyother flame-retardant inorganic additives either in the form of a saltor in the form of metallic oxides, were either not as effective in thesilicone rubber for this purpose, or else could not take the curingtemperatures required for the silicone rubber, or could notadvantageously be used in an application for the silicone rubber, orelse adversely aifected the properties of the cured silicone rubber.

In the specification and in the claims, the convertible methylarylpolysiloxanes, which may be viscous masses or gummy solids,depending on the state of condensation, will hereinafter be referred toas convertible organo polysiloxane or more specifically as convertiblemethyl phenylpolysiloxane. Although convertible organopoly siloxaneswith which the present invention is concerned are now wellknown in theart, for purposes of showing persons skilled in the art the variousconvertible or'ganopolysiloxanes which may be employed in the practiceof the present invention, attention is directed to the abovedescribedconvertible organopolysiloxanes preferably dis;

closed in Sprung Patent 2,484,595, issued October 11, 1949, as well asin Warrick Patent 2,460,795. The aromatic group of the convertibleorganopolysiloxanes may be, e. g., phenyl, tolyl, xylyl, naphthyl,biphenyl, chlorophenyl, tetrachlorophenyl, etc., radicals connected tothe silicon atoms by carbon-silicon linkages. The particular convertibleorganopolysiloxane used in the practice of this invention is critical.Such organopolysiloxanes are advantageously obtained by condensing adiorganodihy-v drolyzable silane, for instance, dirnethyldichlorosilane,with diphenyldichlorosilane, or mixtures of .dimethyldi chlorosilanewith methyl phenyldichlorosilane, etc. (with or without the presence ofsmall amounts of monoorgan'o trihydrolyzable silanes ortriorganomonohydrolyzable silanes, e.g., methyltrichlorosilane,trimethylchlorosilane, etc.), and thereafter effecting condensation ofthe hydrolysis product using a condensing agent, for instance, analkaline condensing agent such as potassium hydroxide, sodium hydroxide,etc., or an acidic condensing agentof the type such as ferric chloride,etc. Alternately, cyclic polymers of dimethyl siloxane with eithercyclic polymers of diphenyl siloxane or cyclic polymers of methylphenylsi'loxane may be intercondensed with, e.g., alkaline condensingagents to give the desired methyl phenylpolysiloxane convertible to thecured, solid, elastic state. The presence of intercondensedmonomethylsiloxy and trimethylsiloxy units, aswell as small amounts ofsilicon-bonded vinyl groups, is not pre-. eluded. No matter how made,the convertible organo-n polysiloxane should contain from 5 to 35 molpercent silicon-bonded aromatic groups. 7 Generally, the convertibleorganoplysiloxane comprises, the recurring structural unit RRSiO where Rand R are selected from the class consisting of methyl and the,aforementioned aromatic halogenated or unhalogenated radicals. Whenmaking the convertible organopolysiloxane by intercondensation, theorganopolysiloxanes from which the heat-curable organopolysiloxanes arepro pared should contain an average of from about 1.98 to 2.01 organicgroups persilicon atom, and that more than; 98 percent of the siliconatoms of the polysiloxane con-3' 3 tain two silicon-bonded organicgroups of the above class. There may be intercondensed with theconvertible organopolysiloxane siloxy units containing from to 2 molpercent silicon-bonded vinyl groups in the form of divinylsiloxy units,methyl vinylsiloxy units, aryl vinylsiloxy units or halogenated arylvinyl siloxy units. Examples of such vinyl siloxy units are as isdescribed, for example, in Marsden Patent 2,445,794, issued July 27,1948.

The cupreous materials employed in the practice of the present inventionare generally those commercially available on the market. The cupreouspowder employed is generally in the form of a finely divided state andpreferably has an average particle size of only a few inicrons. Foroptimum results, from 95 to 100 percent of the particles should gothrough a325-mesh screen when measured by the United States standardsieve series (A.S.T.M. standard). When thus passing through the 325 US.sieve, the average particle size expressed in microns is less than 44microns. A more detailed description of what is meant by U.S. sievemembers is found in US. Patent 2,466,412, issued April 5, 1949, andassigned to the same assignee as the present invention, particularly incolumn 3, line 43. to column 4, line 13 of the said patent.

' In addition to the copper powder which must for optimum results havethe particle size recited above, namely, must be capable of passingthrough a U.S. sieve #325 and has essentially 100 percent of theparticles having an average particle diameter of less than 44 micronsand preferably within the range of 100 percent of the particles havingan average particle diameter of between 1 to 15 or 20 microns, thecupreous material may consist of friable metallic copper core particlessurrounded by protective surface film of cuprous oxide, said film beingrelatively thin as compared with the size of the enclosed copper cores,the amount of cuprous oxide on the. copper particle cores being at leastsuflicient to be identified by present X-ray diffraction methods. Thisparticular cupreous mixture of copper and copper oxides employed in thepractice of the present invention, and methods of preparing the same,are more specifically disclosed and claimed in Hubbell Patent 2,420,540,issued May 13, 1947.

Generally, it is desirable that the cupreous material be employed in thefinely ground state and, for this purpose, it is desirable to use acupreous material having an average, particlev size below about 15microns. Although somewhat coarser particles of a larger averageparticle size may be employed, it is generally desirable to keep theparticle size as fine as possible in order to avoid any adverse effectson the physical properties of the cured organopolysiloxanes, such astensile strength, elongation, and tear strength.

In preparing the compositions herein, defined, various fillers may beemployed as, for instance, finely divided silicas, for instance, silicaaerogel, fume silica, diatomaceous earth, titanium dioxide, lithopone,fillers treated with, e.g., trimethylchlorosilane, etc. The amount offiller employed may be varied widely and may comprise, for instance,from about 25 to 300 percent. of the weight ofthe convertibleorganopolysiloxane. The exact amount of filler employed will depend uponsuch factors as, e.g., the application for which the convertibleorganopolysiloxane is intended, the type of organopolysiloxane andfiller employed, etc.

In order to accelerate the cure of the convertible organopolysiloxane,it is desirable to add to the latter various curing agents, for example,benzoyl peroxide, tertiary butyl perbenzoate, bis-(2,4-dichlorobenzoyl)peroxide,

etc. These curing agents may be present in varying amounts ranging fromabout 0.3 to as high as 6 to 10 percent, by weight, or more, based onthe weight of the convertible organopolysiloxane. Instead of employingchemical curing agents to vulcanize the convertible organopolysiloxane,one may employ high energy electrons in accordance with the processdisclosed and claimed in the above-mentioned Lawton and Buecheapplication Serial No. 291,542.

The flame-retardant compositions herein defined, when employed forcoating purposes, may be coated on by either dipping, knifing, spraying,etc. This may be accomplished by mixing on the usual apparatus, forinstance, dough mixers, etc., or'on rolls, the convertibleorganopolysiloxane, the filler, the cupreous material, and the curingagent, if any, and, if desired, making a mixture of these ingredientswith a solvent for the convertible organopolysiloxane, for instance,toluene, benzene, xylene, etc., to a solids content of about 15 topercent solids. Alternatively, the mixture of convertibleorganopolysiloxane, filler, curing agent, if any, and cupreous materialmay be employed in coating applications without using any dispersing orsolvent phase. This solution-dispersion mixture (in which the liquidphase is preferably a solvent for the organopolysiloxane) or liquid-freemixture can then be applied to various inorganic fibrous substrata, suchas, for instance, glass cloth, asbestos cloth, quartz fiber cloth, etc.,in thin coats of, for example, 2 to 10 mils or more, and thereaftercured at temperatures ranging from about 125 to 200 C. for a timeranging from 5 to 15 minutes. Thereafter, additional curing of thecoated surfaces may be effected by further heat treatment at atemperature of the order of about 200 to 300 C. for a time ranging fromabout a few minutes to even several hours to effect complete conversionof the convertible organopolysiloxane to the substantially infusib-leand insoluble state. Curing with high energy electrons may also beemployed obviating the necessity of using chemical curing agents andheat.

In order that those skilled in the art may better understand how thepresent invention may be practiced, the following examples are given byway of illustration and not by way of limitation. All parts are byweight.

The test for flame retardancy which included determination of theburning time and percent sample consumed was carried out as follows: Aspecimen of the cured, filled and modified organopolysiloxane, 0.075 x0.5 x 6" was suspended Vertically in a glass tube (2 inside diameter by6" long) by means of a wire pierced through the center 0.5 inch from thetop of the specimen.

A Bunsen burner flame (approximate temperature 2000' F.) was placed sothat the lower 0.75 of the specimen was in the center of the flame.After the specimen had been in the flame for 20 seconds, the burner wasremoved and the duration of burning was timed. The sample was consideredas burning until all visible glowing had ceased. The sample was thenremoved from the glass tube and struck sharply at least three timesagainst a hard, flat surface. The proportion of the sample remainingafter these blows was used to determine the unburned volume of thesample. For optimum suitability, the burning time should be below 110seconds and percent consumed be: low 50 percent. A

The finely divided copper, cupric oxide, cuprous oxide, and cuprouschloride employed in the following examples had an average particle sizeof about 10 to 25 microns. The copper powder used and identified asCopper Powder contained small amounts of cuprous oxide, about of thecopper powder passing through a 325-meshf screen, as described above.For comparison purposes, in the following ex amples, other metallic andinorganic materials such as antimony oxide, nickel carbonate, coppercarbonate CuC O .Cu(OH') aluminum powder, glass fusing frit;

EXAMPLE 1 6 employing the same finely divided copper of Example TableIII below, in which the values shown for the various ingredients areparts, by weight, shows the formulations employed in each instance.Table III also shows A heawurable, tolueneusoluble organopolysfloxanethe properties of the various fongnulations after they were vertible tothe cured, solid, elastic state was obtained by mowed for mP at 2 and ft for condensing 100 parts octamethylcyclotetrasiloxane with Y f of timeas stlpPlated at 150 mclud parts octaphenylcyclotetrasiloxane in thepresence of 9 m some msiances h tePS11e,and elongation Proper about Q01part KOH until a highly Viscous mass border t1es, together with burmngtime 1n seconds and the pering on a gummy solid was obtained. Thisproduct had 10 K samplefonsumed 111 each lnstancles All the P QP a ratioof approximately two total methyl and phenyl ties recited n Table IIIfor sample Nos. 18, 19 and groups per silicon atom and contained about53 mol pep were determined after heat-aging the molded samples for centsilicon-bonded phenyl groups. Various formulations 1 hour at 9 All thePrPPemes Sample 21 were prepared from this convertible methyl phny1po1ywere determined aftenheat-aging the molded samples for siloxane, inwhich cupreous additives, including the cop- 15 2 hours at 150 Whlle allthe PP for Sample per and coppepcqpper Oxide mixtures of the instant 22were detenmlnesl after heat-aglng the molded samples vention, wereincorporated in varying proportions. Other for 17 hours at 1501modifying agents, which will be hereinafter identified, Tabl III werealso tested as additives 1n this convertible organepolysiloxane, forflame-retardant properties. The basic 20 Sample Number formulationemployed, exclusive of flame-retardant addi- Ingredient tive, andidentified as Formulation 1 was composed of 18 19 20 21 22 100 parts ofthe convertible methyl phenylpolysiloxane,

45 parts silica aerogel (Santocel CS and 2.0 parts ben o e tible methylphenylpolysilox zoyl peroxide. Each formulation was molded into flat 25a fl g p e 125 125 96 82 82 sheets for 10 minutes at 127 C. and thenheated in an 3 ;333: 25 3 $8 $2 air-circulating oven for 1 hour at 150C. The followhiatomaceousearth 12 as ing Table I shows the additive usedand relative proporfigfg giigfifii a Q {i if: i? tions of additiveemployed. Table I also shows the flameg a lz, a 835 900 845 '960 1 835retardant properties of the various cured materials( which $3H Z3 22 3253 28 were tested for burning time and percent of sample con- Percentconsumed 25 17 0 10 7 sumed after heat-aging for 1 hour at 150 C.").

Table I Formula- Percent Seconds Percent Sample No. tion N o. AdditiveAddi- Burning Contive 1 Time sumed 1 5 64 100 1 20 120 100 1 s 147 70 41 NiOO; 20 141 75 5 1 CuGO .Ou(OH) 5 139 100 6 1 Glass fusing frit 22163 100 1 1. ZnGO; s 160 8 1 21100 20 125 50 Q- 1 Aluminumpowden; 5 21060 10,, 1 an 20 180 100 11 1 Copper powder 1 64 20 12 1 1 do 2 73 20 131 4 74 20 14 1 5 66 25 15.- p 1 10 77 35 1s 1 20 102 30 17 (Continua; 1236 100 1 Based on weight of convertible methylphenylpolysiloxane. 1 3Alter 4 hours at; 150 C. 1

The physical proper-ties of sample Numbers 11, 12, 13 EXAMPLE 3 andcontrol sample No. 17 were established, particularly the tensilestrength and elongations after the initial molding cycle followed by aheat treatment for 1 hour at 150 C. Table II shows the results of thesephysical tests.

Table II 1 hl./150 C.

Sample No.

Tensile, Percent p.s.i. Elongation EXAMPLE 2 This example illustratesthe use of the filled silicone gum employed in Example 1 in which finelydivided titanium dioxide, and in some instances finely divideddiatomaceous earth (Celite Superfioss), were also added,

polysiloxane employed in Examples 1 and 2, and 4%, by

weight, was a straight methylpolysiloxane gum obtained by condensingoctamethylcyclotetrasiloxane with a small amount of an alkalinecondensing agent in the same manner as that described in Example 1 toyield a methyl polysiloxane gum containing an average of about twomethyl groups per silicon atom. This mixture of methylphenylpolysiloxa-ne and methylpolysiloxane gums will hereinafter bereferred to as mixed convertible organ'opolysiloxanes. Samples weremolded of formulations shown in the following Table IV for 10 minutes at127 C. and then heat-treated for 1 hour at C. The finely divided silicaused as the main filler with the mixedconvertible organopolysiloxaneswas a fume silica identified as Cab-0--Sil and sold by Godfrey L.Cabot,1Inc.

of Boston, Massachusetts. All the values recited in Table IV are partsby weight. The cupreous material used in this example was the finelydivided copper powder used in Example 1.

Table IV C Sample Number Ingredient Mixed convertible organo- 120 120120 120 170 200 55 55 55 55 75 90 TiO 2. 2. 5 4. 5 7. 5 30 42Diatomaceous earth. 60 Benzol peroxide 2. 1 2. 1 2. 1 2. 1 2. 9 3. 5Copper powden. 1. 35 1. 8 1. 35 1. 35 2. 5 4. 5 Quartz fibers 27 37. 8Tensile strength, p. 1, 120 725 850 880 800 715 Percent elongation. 380230 260 255 290 190 Burning time, seconds.- 64 55 64 68 66 79 lPercentconsumed. 5 V 5 5 15 15 16 EXAMPLE 4 In this example, a gum formulationwas prepared from 100 parts of the mixture of convertibleorganopolysiloxanes described in Example 3 (of which 96 parts was themethyl phenylorganopolysiloxane and 4 parts was the methylpolysiloxane),42 parts fume silica, parts diatomaceous earth, 2 parts of titaniumdioxide and 2.9 parts bis(2,4-dichlorobenzoyl) peroxide. This materialwas identified as formulation No. 2." Employing formation No. 2, threemolding compounds were prepared in which the following Table V shows theingredie. ents used, together with the proportions of said ingredients.The cupreous material used in one instance comprised the copper powderemployed in Example 1, while in another instance the cupreous materialcomprised cupric Y oxide (CuO). A control was also compounded in whichthe cupreous material was omitted entirely from the formulation. Aftermaking up the various compounds, they were molded into the form of flatsheets at 127 C. for about 10 minutes and thereafter heat-aged in anoven for five hours at 150 C. and then tested for tensile strength,percent elongation, burning time and percent consumed. The followingTable V also shows the results of the various tests conducted on themolded and heat-treated samples.

EXAMPLE 5 To 100 parts of formulation No. 2, more particularly describedin Example 3, were added 10 parts additional diatomaceous earth, 10.8parts titanium dioxide and 1.5 parts cuprous oxide (Cu O). The mixtureof ingredients was then molded into the form of flat sheets for 10minutes at 127 C. and thereafter heat-treated for 4 hours at 150 C. andthen 4 hours at 250 C. in an oven, and samples thereof tested forburning time and percent consumed, in the manner described in the aboveexamples. As a result of these tests, it was found that the burning timefor the sample was 102 seconds and the pereentconsumed was 15%.

EXAMPLE 6 V This example illustrates the eifect of employing a cupreousmaterial in combination with a convertible organopolysiloxane which isfree of silicon-bonded aromatic, for instance, silicon-bonded phenylgroups. More particularly, a convertible polydimethylsiloxane obtainedby condensing octamethylcyclotetrasiloxane with about 0.01%, by weight,potassium hydroxide at elevated temperatures until a high molecularweight viscous material (about 4 to 6 million centistokes when measuredat about 38 C.) was obtained. To parts of this convertiblemethylpolysiloxane (which had a ratio of about two methyl groups persilicon atom) were added on compounding rolls 42 parts silica aerogeland 1.65 parts benzoyl peroxide. To 100 parts of this mixture ofingredients were then added 1.75 parts cupric oxide. The sample wasmolded for 10 minutes at 127 C. and then heat-treated for 24 hours at250 C. and then tested for burning time and percent consumed. Thesetests showed that the burning time was of the order of seconds and thatit was 100% consumed.

EXAMPLE 7 To 100 parts of formulation No. 2, described in Example 4,were added 1.75 parts of various finely divided additives includingcopper, cupric oxide, and cuprous chloride. A control was also preparedusing formulation No. 2 alone and omitting any additive. Each of thesesamples was molded in the form of flat sheets for 10 minutes at 127 C.and thereafter given an additional heat-treatment comprising four hoursat C. in an air-circulating oven. The following Table VI shows theadditive used, the percent additive, the burning time in seconds, andthe percent consumed for each sample. Table VI Parts Burning PercentSample No. 7 Additive Additive Time, Oon- Seconds sumed,

It will, of course, be apparent to those skilled in the art that insteadof using the particular organopolysilom ane containing silicon-bondedaromatic radicals, forinstance, phenyl radicals, described above, otherorganopolysiloxanes containing different silicon-bonded aro-. maticradicals, or silicon-bonded phenyl radicals in different proportions,many examples of which aromatic radicals have been given above, may beemployed without departing from the scope of the invention. Theproportions of ingredients may be varied widely, especially the fillersand the curing agents and other types of curing agents, such as tertiarybutyl perbenzoate may also be employed. The amount of cupreous materialused may be varied within fairly wide limits but is advantageouslywithin the range of from about 0.25 to 20%,- preferably within the rangeof from about 0.5 to 10%, by weight, based on the weight of theconvertible organopolysiloxane.

In addition to the cupreous materials recited in the above examples, onemay also use, for instance,"mixtures of copper and copper oxide, mixedsalts of copper and copper oxide or mixed salts of copper chloiideandcopper oxide (e.g., cupric oxychloride), other copper halides, forinstance, cupric chloride, cuprous fluoride, cupric bromide, etc. Incertain applications where it is desirable that the color of the curedsilicone rubber be white or free of any undesirable coloration, it hasbeen found that the copper and cupric oxide types of cupreous materialsare preferred since materials such .as the cupric mcnprous chloride tendto impart a greenish tinge to thecurable, filled compound in which it ispresent and this tinge isdeepened to a darker green :upon heat curing.However, in applications where color is of no importance or where it canbe acceptably masked, the copper halides can usually be satisfactorilyemployed.

Various uses can be made of the compositions herein described. Thus, thecompounds of the invention can be used for insulating electricalconductors by extruding the silicone rubber compound containing thecupreous material onto a metallic conducting core (e.g., copper,aluminum alloys of copper, etc.) and thereafter heattreating theinsulated conductor at elevated temperatures in an oven or in steamuntil vulcanizations is efiected. Conductors so formed areflame-resistant and can withstand elevated temperatures for long periodsof time, more so than insulated conductors in which the cupreousmaterial is absent.

Other applications in which the claimed invention can be employed whereresistance to extremely high temperatures are. desirable and whereordinary silicone. rubbets will ignite and continue to burn, are ingaskets, grommets, seals, heater ducts, protective ins-ulations, varioustypes of equipment such as wrap-around tapes for elements which may besubjected to elevated temperatures, etc. Dispersions .ordispersion-solutions of the materials embraced by the instant inventioncan be used to coat various heat-resistant cloths such as asbestoscloth, glass cloth, etc., and these wound around. mandrels to makevarious tubes or conduit material useful in conducting heat to varioussectionsof an airplane. One particular application for which theinvention herein described is exceptionally suitable is in connectionwith flaps to be employed for tents which are intended to house stoveswhose chimneys have exits through the top of the tent. Obviously, theusual tent material will not withstand the high temperatures immediatelyadjacent such chimneys. However, by inserting at this point a section ofthe flameretardant silicone rubber described in the present application,it is possible to obviate the danger of fires, which may spread to thebalance of the tents should the chimney of the stove become overheatedfor any reason.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. A composition of matter which in the cured state exhibits improvedflame-retardant properties, which composition comprises (1) anorganopolysiloxane convertible to the cured, solid, elastic stateconsisting essentially of silicon atoms, oxygen atoms, methyl groups,and an aromatic radical selected from the class consisting of aryl andhalogenated aryl radicals, the said organopolysiloxane containing from 3to 35 mol percent silicon-bonded aromatic groups, there being presentfrom 1.98 to 2.05 total organic groups per silicon atom, (2) a finelydivided inorganic filler, the filler comprising from. 25 to 300 percent,by weight, based on the weight of the convertible organopolysiloxane,(3) from 0.25 to 20 percent, by weight, based on the weight of (l) afinely divided cupreous material present in an amount sufiicient toimpart flame-retardant properties to the cured, solid, elasticorganopolysiloxane, the said cupreous material being selected from theclass consisting of copper, copper oxides, copper halides, and mixturesof the aforesaid cupreous materials, and (4) a peroxy curing agent for(l).

2. The cured product of claim 1.

3. A composition as in claim 1 in which the filler is a finely dividedsilica filler.

4. A composition of matter which in the cured state exhibits improvedflame-retardant properties, which composition comprises (I) anorganopolysiloxone convertible to the cured, solid, elastic stateconsisting essentially of silicon atoms, oxygen atoms, methyl groups,and an aromatic radical selected from the class consisting of aryl andhalogenated aryl radicals, the said organopolysilox- 10 ane containingfrom 3 to 35 mol percent silicon-bonded aromatic groups, there beingpresent from 1.98 to 2.05 total organic groups per silicon atom, (2) afiller comprising finely divided silica, the silica comprising from 25to 300 percent, by weight, based on the weight of the con, vertibleorganopolysiloxane, 3) from 0.25 to 20 percent, by weight, based on theweight of (1) of a finely divided cupric oxide present in an amountsufficient to impart flame-retardant properties to the cured, solid,elastic organopolysiloxane, and (4) a peroxy curing agent for (1).

5. A composition of matter which in the cured state exhibits improvedflame-retardant properties, which composition comprises (1) a methylphenylpolysiloxane convertible to the cured, solid, elastic stateconsisting essentially of silicon atoms, oxygen atoms, methyl groups andphenyl groups, the said methyl phenylpolysiloxane containing from 3 to35 mol percent silicon-bonded phenyl groups and there being present from1.98 to 2.05 total methyl and phenyl groups per silicon atom, (2) afinely divided silica filler, the filler comprising, by weight, from 25to 300 percent of the weight of the convertible methylphenylpolysiloxane, (3) from 0.25 to 20 percent, by weight, based on theweight of (1) of a finely divided cupreous material present in an amountsuificient to impart flameretardant properties to the cured, solid,elastic organopolysiloxane, the said cupreous material being selectedfrom the class consisting of copper, copper oxides, copper halides, andmixtures of the aforesaid cupreous materials, and (4) a peroxy curingagent for (l).

6. The cured product of claim 5.

7. A composition of matter which in the cured state exhibits improvedflame-retardant properties, which com position comprises (1) a methylphenylpolysiloxane convertible to the cured, solid, elastic stateconsisting essentially of silicon atoms, oxygen atoms, methyl groups andphenyl groups, the said methyl phenylpolysiloxane containing from 3 to35 mol percent silicon-bonded phenyl groups and there being present froml.98 to 2.05 total methyl and phenyl groups per silicon atom, (2) afinely divided silica filler, the filler comprising, by weight, from 25to 300 percent of the weight of the convertible methyl phenylpolysiloxane, (3) from 0.25 to 20 percent, by weight, based on theWeight of (l) of finely divided cupric oxide, and (4) benzoyl peroxide.

8. The heat-treated product of claim 7.

9. A composition of matter which in the cured state exhibits improvedflame-retardant properties, which composition comprises (1) a methylphenylpolysiloxane convertible to the cured, solid, elastic stateconsisting essentially of silicon atoms, oxygen atoms, methyl groups andphenyl groups, the said methyl phenylpolysiloxane containing from 3 to35 mol percent silicon-bonded phenyl groups and there being present froml.98 to 2.05 total methyl and phenyl groups per silicon atom, (2) afinely divided silica filler, the filler comprising, by weight, from 25to 300 percent of the weight of the convertible methylphenylpolysiloxane, (3) from 0.25 to 20 percent, by weight, based on theweight of (l) of finely divided cupric oxide, and (4)bis(2,4-dichlorobenzoyl) peroxide.

10. The heat-treated product of claim 9.

11. A composition of matter which in the cured state exhibits improvedflame-retardant properties, which composition comprises (1) a methylphenylpolysiloxane convertible to the cured, solid, elastic stateconsisting essentially of silicon atoms, oxygen atoms, methyl groups andphenyl groups, the said methyl phenylpolysiloxane containing from 3 to35 mol percent silicon-bonded phenyl groups and there being present from1.98 to 2.05 total methyl and phenyl groups per silicon atom, (2) afinely divided silica filler, the filler comprising, by weight, from 25to 300 percent of the weight of the convertible methylphenylpolysiloxane, (3) from 0.25 to 20 percent, by weight, based on theweight of (l) of finely divided copper, and (4) a peroxy curing agentfor (l).

12. A composition of matter which in the cured state exhibits improvedflame-retardant properties, which -com-' position comprises (1) a methylphenylpolysiloxane convertible to the cured, solid, elastic stateconsisting essentially of silicon atoms, oxygen atoms, methyl groups andphenyl groups, the said methyl phenylpolysiloxane containing from 3 to35 mol percent silicon-bonded phenyl groups and there being present from1.98 to 2.05 total methyl and phenyl groups per silicon atom, (2) afinely divided silica filler, the filler comprising, by weight, from 25to 300 percent of the weight of the convertible methylphenylpolysiloxane, (3) from 0.25 to 20 percent, by weight, based on theWeight of (1) of cuprous oxide, and (4) a peroxy curing agent for (l).

13. A composition of matter which in the cured state exhibits improvedflame-retardant properties, which composition comprises (1) a methylphenylpolysiloxane convertible to the cured, solid, elastic stateconsisting essentially of silicon atoms, oxygen atoms, methyl groups andphenyl groups, the said methyl phenylpolysiloxane containing from 3 to35 mol percent silicon-bonded phenyl groups and there being present from1.98 to 2.05 total methyl and phenyl groups per silicon atom, (2) afinely divided silica filler, the filler comprising, by weight, from 25to 300 percent of the Weight of the convertible methyl phenylsiloxane,(3) from 0.25 to 20 percent, by weight, based on the weight of (1) ofcuprous chloride, and (4) a peroxy curing agent for (l).

14. The process for improving the flame-retardant properties of a filledorganopolysiloxane convertible to the cured, solid, elastic stateconsisting essentially of silicon atoms, oxygen atoms, methyl groups andan aromatic radical selected from the class consisting of aryl andhalogenated aryl radicals, the said organopolysiloxane containing from 3to mol percent silicon-boiided aromatic groupsv and from 0 to 2 molpercent siliconbonded vinyl groups, there being present from 1.98 to2.05 organic groups per silicon atom, and the filler for theorganopolysiloxane comprising, by weight, from 25.to 300 percent of theweight of the convertible organopolysiloxane, which process comprisesincorporating in the aforesaid filled organopolysiloxane from 0.25 to'20 percent, by weight, based on the weight of the organopolysiloxane ofa cupreous material selected from the class consisting of copper, copperoxides, copper halides and mixtures of the aforesaid cupreous materials,and a peroxy curing agent. i j

15. The process as in claim 14 in which the convertibleorganopolysiloxane is a methyl phenylpolysiloxane and the cupreousmaterial is cupric oxide. I f

16. The process as in claim 14 in which the convertibleorganopolysiloxane is a methyl phenylpolysiloxane and the cupreousmaterial is a mixture of copper, and cup'ric oxide.

17. The process as in organopolysiloxane is a methyl phenylpolysiloxaneand the cupreous material is finely divided copper.

References Cited the file of this patent UNITED STATES PATENTS 2,480,620Warrick Aug. 30, 1949 2,593,817 Waggoner Apr. 22, 1952 2,645,588 BarryJuly 14, 1953' 2,650,206 Stock Aug. 25, 1953 2,684,349 Welton July 20,1954 claim :14 in which the convertible

1. A COMPOSITION OF MATTER WHICH IN THE CURED STATE EXHIBITS INPROVEDFLAME-RETARDANT PROPERTIES, WHICH COMPOSITION COMPRISES (1) ANORGANOPOLYSILOXANE CONVERTIBLE TO THE CURED, SOLID, ELASTIC STATECONSISTING ESSENTIALLY OF SILICON ATOMS, OXYGEN ATOMS, METHYL GROUPS,AND AN AROMATIC RADICAL SELECTED FROM THE CLASS CONSISTING O ARYL ANDHALOGANATED ARYL RADICALS, THE SAID ORGANOPOLYSILOXANE CONTAINING FROM 3TO 35 MOL PERCENT SILICON-BONDED AROMATIC GROUPS, THERE BEING PRESENTFROM 1.98 TO 2.05 TOTAL ORGANIC GROUPS PER SILICON ATOM, (2) A FINELYDIVIDED INORGANIC FILLER, THE FILLER COMPRISING FROM 25 TO 300 PERCENT,BY WEIGHT BASED ON THE WEIGHT OF THE CONVERTIBLE ORGANOPOLYSILOXANE, (3)FROM 0.25 TO 20 PERCENT, BY WEIGHT, BASED ON THE WEIGHT OF (1) A FINELYDIVIDED CUPREOUS MATERIAL PRESENT IN AN AMOUNT SUFFICIENT TO IMPARTFLAME-RETARDANT PROPERTIES TO THE CURED, SOLID, ELASTICORGANOPOLYSILOXANE, THE SAID CUPREOS MATERIAL BEING SELECTED FROM THECLASS CONSISTING OF COPPER, COPPER OXIDES, COPPER HALIDES, AND MIXTURESOF THE AFORESAID CUPREOUS MATERIALS, AND (4) A PEROXY CURING AGENT FOR(1).